Quantitative Study of the Elastic Modulus of Loosely Attached Cells in AFM Indentation Experiments  Maxim E. Dokukin, Nataliia V. Guz, Igor Sokolov  Biophysical Journal  Volume 104, Issue 10, Pages 2123-2131 (May 2013) DOI: 10.1016/j.bpj.2013.04.019 Copyright © 2013 Biophysical Society Terms and Conditions

Figure 1 Schematics of the interaction between an AFM spherical indenter (probe) and (a) firmly and (b) loosely attached cells. Deformations of both the cell body and surrounding cellular brush are shown. Z is the relative position of the cantilever; d is the cantilever deflection; Z0 is nondeformed position of the cell body; i, itop, and ibottom are the deformations of the cell body; h and htop are the separation distances between the cell body and the probe; and hbottom is the distance between the cell body and substrate. Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 2 Representative optical images of firmly (well-spread images) and loosely (spherical images) adhered cells. (Right panel, inset) Confocal side view of both well-spread and spherical-looking cells. Confocal images are not to scale (the heights of cells in the confocal images are between 10 and 20 μm). Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 3 A representative example of the processing of the force-indentation curves for the case of firmly adhered cells. (a) Raw data and partial fitting of the curve with Eqs. 1 and 2. The fitting parameters were Z0 and the Young’s modulus; (b) dependence of the derived Young’s modulus on the indentation depth; and (c) fitting of the cellular brush with Eq. 4 (done and shown for 0.2 < h/L < 0.9). Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 4 A representative example of the processing of the force-indentation curves for the case of loosely adhered cells. (a) Raw data and partial fitting of the curve with Eqs. 6 and 7. The fitting parameters were Z0 and the Young’s modulus; (b) dependence of the derived Young’s modulus on indentation; and (c) fitting of the cellular brush with Eq. 11 (done and shown for 0.2 < h/L < 0.9). Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 5 The distribution of the Young’s modulus calculated using the brush models for (a) firmly and (b) loosely attached cells, and using Hertz model for (c) firmly and (d) loosely attached cells. Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 6 A representative example of processing of raw force data (Z versus d) with the Hertz model (Eq. 12). Scattered points represent the raw experimental data. (a) Fitting on the entire range of forces. (b) Fitting of the initial part of the force curve (small deflections/forces; see dashed line for the mathematical extrapolation outside the fitting region). (c) Dependence of the Young’s modulus derived with the Hertz model on the indentation depth. Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions

Figure 7 Distributions of the brush length (L) and grafting density (N) are shown for (a and c) firmly attached and (b and d) loosely attached cells, respectively. Biophysical Journal 2013 104, 2123-2131DOI: (10.1016/j.bpj.2013.04.019) Copyright © 2013 Biophysical Society Terms and Conditions